Conventional control of the superchargers has been carried out in response to accelerator (pedal) position or throttle opening. Accordingly the conventional control has disadvantages in that supercharging cannot be effected even when it is needed in view of the state of the accelerator or supercharging cannot be stopped even when it is not necessary.
Namely, such disadvantages entail further drawbacks that a sufficient supercharging performance corresponding to the supercharging ability cannot be attained and that unnecessary supercharging brings about waste in fuel consumption.